Contact clamp



April 27, 1965 E. GARBER ETAL CONTACT CLAMP Filed July 3, 1963 INVENTORS ER WIN GARG KLAUS ECKA 7' BY ATTORNEY United States Patent 3,181,197 CGNTAQT CLAMP Erwin Garber, Stuttgart-Zutienhausen, and Klaus Ecirardt,

Stuttgart-Unterturirheirn, Germany, assignors to International Standard Electric Corporation, New York, N .Y., a corporation of Delaware 7 Filed July 3, 1963, Ser. No. 292,668 7 Claims priority, application Germany, July 11, 1962, St 19,470 1 Claim. (Q1. 339-97) When working with electrical apparatus, especially in laboratories and test shops, electrical conductors of different diameters often have to be connected to clamping devices. To this end it is common practice to use the so-called instrument clamps. insulated conductors, however, it is always newssary to strip the insulation of the conductors at the clamping point. In cases where such insulated instruments must be continuously brought into contact with clamps, the described and conventional type of clamping connection is time-consuming and unreliable. This unreliability also appears in the case of lacquered wires whose layer of lacquer is of a somewhat transparent kind, from which it is often difiicult to recognize whether the lacquer has been sufiiciently removed, or whether there are still small remainders of the layer of lacquer which are just suficient to prevent an electrical contact from being established in the clamp.

The present invention is based on the problem of providing a contact clamp which not only permits a very rapid establishment of contacts, especially by doing away with the necessity of having to tighten screws, but is also supposed to serve the establishment of an electrical connection with an insulated conductor without the insulation having to be specially removed or stripped at the point of contact. Moreover, such a contact clamp was supposed to be manufactured by using commercially available semi-manu-factured products without having to produce the thread and the associated nut which are normally used for the clamping purpose.

To solve this problem the invention proposes a clamp which is easy to manufacture and suitable for establishing contacts with insulated conductors without it being necessary to strip the insulating sheathings, and which is supposed to be characterised by an appropriately silvercoated contact-blade holding device having the shape of a bar, e.g. a four-cornered or square steel bar, including at least two longitudinal surfaces meeting against one another with their longitudinal sides, and constituting an angle, especially a right angle, on which, by lying next to each other in the longitudinal direction, there is arranged a pair of sharp-edged ground or cut contact blades, which especially have the shape of flat steel springs provided with sharp edges resulting from the cutting or stamping, preferably of stainless steel, and which are mounted on to the lower end of the bar comprising the mounting means, e.g. with the aid of screws or rivets, and further characterised in that the nonmounted ends of the two fiat springs permitting an elastical deflection, and projecting over the top end of the bar, are rounded-oft at the upper corners of the fiat springs facing one another, simultaneously constituting an angle of introduction for pressing-in the insulated conductor without atfecting the sharpness of the edges of the fiat springs.

FIGURE 1 is a side elevational view oi the contact clamp.

FIGURE 2 is a perspective view and shows the mounting of the springs on the bar of the contact clamp.

FIGURE 3 is a transverse vertical section of the contact clamp at the point of contact with an inserted wire.

The invention will now be explained in detail with reference to FIGS. l-3 of the accompanying drawing. FIG.

Prior to the mounting of 7 ice -1 shows a four-cornered or square steel bar 1 comprising, at point 2 on its lower end, mounting means with the aid of which the clamp may either be riveted or screwed to a support. On two neighbouring surfaces the bar carries the two flat springs 3 which, in direction towards the lower end of the bar, are mounted with the aid of the screws at points 4 and 5, to the four-cornered or square steel bar appropriately with a slight initial stress. In some cases it may be advisable to mount the flat springs at this point with the aid of rivets. In the upper par of the bar 1, the fiat springs are capable of being elastically deflected. According to the showing of FIG. 2, for ex- 7 ample, a conductor 6 provided with an insulation consisting of a layer of lacquer, may be pushed from above into the position 7. In the course of this the two flat springs 3 are spread or pushed apart, and the neighbouring lon itudinal edges of the two flat springs are caused to cut the insulation by acting as the cutting edges of a knife, and also scratch the copper conductor, thus establishing the electrical contact at two points. In order to prevent the insulated conductor which is inserted into this contact clamp, from being obstructed in the inserted state by the upper end of the bar 1, this bar is provided at its upper end with a guide slot 8 which is determined by the angle bisector of the angle constituted by the two flat springs. The depth of introduction is limited by a slot, the cutting-0E is prevented,.and the conductor is retained. in position at a favourable cutting angle.

FIG. 3 shows a sectional view of the inventive type of arrangement at the point of contact. recognized how the two flat springs 3 are lifted out of their normal position for cutting the insulation sheathing 9 of the conductor it with their adjacent sharp edges, in order to establish the electrical contact.

' The spring tension of the initially stressed contact blades, if possible, should remain the same throughout the entire depth of introduction. A blade which is long with respect to the depth of introduction would satisfy this demand most suitably. permitted by the depth of introduction necessary for outting the insulation. An approach to meeting this demand can be made when providing a still suiiicient spacing or distance between the point of introduction and the contact point, i.e. when letting the airgap between the blades, from the point of introduction to the clamping point at the bottom or" the slot of the blades, run somewhat apart. These measures have a direct influence upon the value of the contact resistance. These measures also serve to provide the wire with a definite position and, consequently, with a definite connecting pressure. The deviations of the contact resistance which may be due' to repeated introductions of a wire may, in this way, be kept at a minimum.

The flat springs according to FIGS. 1 and 2 are in such a way rounded 0d at points 11, that the rounded- Most appropriately, the bar 1 of the contact clamp is made from a customary four-cornered or square material. Theflat springs 3 may be cut in a simple way from a strap material having a suitable width, with the edges of these fiat springs, without requiring any further processing, already having the sharpness necessary for cutting the insulating sheathing. The nar-rowedges of the hat springs'may also be ground.

Clamps of this kind provide particularly great advantages with respect to time especially in cases Where, for example, many hundreds of insulated. conductors must be continuously connected and disconnected electrically. This is often the case in test shops of cable-manufacturing plants Where e.g. many hundred-pair types of telecommunication cables have to be examined or tested with artist It will be easily a This, however, is spatially not not be reduced any further.

circular or square cover plate of a switching desk, whereupon the individual Wires, after the cable sheathing has been stripped, are radially bent outwards to the contact clamps. The inventive types of contact clamps are very suitable for being firmly mounted'to the cover plate of such testing instruments, because they require very little space for special manipulations, such as the screwing 0r tightening of nuts or screws and may, therefore, be arranged very close to one another. 1 s

The slots 8 of the clamp bar are aligned radially in relation to the centre of the cover plate, or in the direction of an introduced (inserted) wire.

By using the inventive type of contact clamp it is possible to reliably establish many hundreds of electrical contacts'among insulated conductors within a period of time which canit is particularly useful that the contact clamp, on account of its strong cutting effect which is due to its construction, is capable of cutting insulating sheathings of all kinds, such as lacquered or varnished insulation, insulation sheathings of polyvinyl chloride, polyethylene and other plastic materials, rubber insulation, and of course also the well-known paper-string, insulation of telecommunication cables.

invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of our invention as set forth in the objects thereof and in the accompanying claim.

What We claim is: s

A clamp for establishing electrical contact wih insulated conductors comprising a bar having at least two surfaces angularly disposed to each other, first and second contact blades disposed on said surfaces in angular relation to each other, the ends of said contact blades projecting over the end of said bar and being tapered at the junction of said contact blades to provide an entry for a conductor to be moved downwards between said blades, the edges of said blades making contact With the conductors being sharp to cut through the insulation of the-conductors to make contact with the conductor, and a slot in the end of said bar dividing the angle between said contact blades for guiding the conductor and limiting the depth of insertion of the conductor.

References Cited by the Examiner UNITED STATES PATENTS 1,948,309 2/34 Neumann 339-97 2,333,266 11/43 Miller 339- -95 2,539,230 1/51 Craig 339-205 2,947,965 8/60 Scoville 33995 2,983,892 5/61 Williams et al. 339258 X 3,027,536 3/62 Pasternak 339-97 JOSEPH D. SEERS, Primary Examiner.

M. HENSON WOOD, 1a., Examiner. 

